U.S. Pat. No. 7,132,581 concerns processes for converting oxygenates to olefins that include a step of pretreating catalyst used in the conversion reaction. A fresh or regenerated metalloaluminophosphate molecular sieve, which is low in carbon content, is pretreated with an aldehyde. The aldehyde forms a hydrocarbon co-catalyst within the pore structure of the molecular sieve, and the pretreated molecular sieve containing the co-catalyst is used to convert oxygenate to an olefin product.
U.S. Pat. No. 7,057,083 relates to processes for converting oxygenates to olefins that include a step of pretreating molecular sieve used in the conversion reaction with a C4-C7 olefin composition, which contains one or more C4-C7 olefins. Fresh or regenerated molecular sieve, which is low in carbon content, is contacted or pretreated with the olefin composition to form a hydrocarbon co-catalyst within the pore structure of the molecular sieve, and the pretreated molecular sieve containing the co-catalyst is used to convert oxygenate to a lighter olefin product.
U.S. Pat. No. 6,844,476 describes a method for converting heavy olefins present in a product stream exiting a first reaction zone into light olefins and carbonaceous deposits on a catalyst without separation of the heavy olefins from the product stream exiting the first reaction zone. The method comprises creating the product stream exiting the first reaction zone, the product stream exiting the first reaction zone comprising the heavy olefins, moving the product stream exiting the first reaction zone to a second reaction zone without separation of the heavy olefins from the product stream exiting the first reaction zone, and contacting the product stream exiting the first reaction zone with the catalyst under conditions effective to form the light olefins, the contacting causing the carbonaceous deposits to form on at least a portion of the catalyst.
US20060161035 describes the average propylene cycle yield of an oxygenate to propylene (OTP) process using a dual-function oxygenate conversion catalyst is substantially enhanced by the use of a combination of:
1) moving bed reactor technology in the catalytic OTP reaction step in lieu of the fixed bed technology of the prior art;
2) a separate heavy olefin interconversion step using moving bed technology and operating at an inlet temperature at least 15° C. higher than the maximum temperature utilized in the OTP reaction step;
3) C2 olefin recycle to the OTP reaction step; and
4) a catalyst on-stream cycle time of 700 hours or less. These provisions hold the build-up of coke deposits on the catalyst to a level which does not substantially degrade dual-function catalyst activity, oxygenate conversion and propylene selectivity, thereby enabling maintenance of average propylene cycle yield for each cycle near or at essentially start-of-cycle levels.
U.S. Pat. No. 5,914,433 relates to a process for the production of light olefins comprising olefins having from 2 to 4 carbon atoms per molecule from an oxygenate feedstock. The process comprises passing the oxygenate feedstock to an oxygenate conversion zone containing a metal aluminophosphate catalyst to produce a light olefin stream. A propylene stream and/or mixed butylene is fractionated from said light olefin stream and butylenes and heavies cracked to enhance the yield of ethylene and propylene products. This combination of light olefin product and butylene and heavies cracking in a riser cracking zone or a separate cracking zone provides flexibility to the process which overcomes the equilibrium limitations of the aluminophosphate catalyst. In addition, the invention provides the advantage of extended catalyst life and greater catalyst stability in the oxygenate conversion zone. In said process the effluent of the riser cracking zone or the separate cracking zone is sent to the oxygenate conversion zone.
It has now been discovered a more efficient process to make light olefins, in particular propylene and aromatics from oxygenates. This invention relates to a process including three zones: a XTO reaction zone containing catalyst wherein “X” (e.g. oxygenates) are converted into mainly light olefins, an OC reaction zone containing substantially the same catalyst wherein heavier olefins and optionally ethylene are converted into aromatics and additional light olefins and a zone wherein the catalyst used in the other two zones is regenerated (the catalyst regeneration zone also referred as the regeneration zone). This invention relates to processes for converting oxygenates to olefins over a zeolite-based catalyst (in the XTO reaction zone) that include a step of primarily using the zeolite-based catalyst in the conversion reaction (the OC reaction zone) with a substantially olefinic feedstock, which contains one or more C2-C12 olefins, and forming by way of example 0.1 wt % or more of coke-like deposition on the molecular sieves. The main role of this hydrocarbons deposition is in selective deactivation of the non-selective acid sites. This contact of the molecular sieve with an olefinic feedstock could be performed in the presence or in absence of water and oxygenated compounds. In a most preferred embodiment, this contact is performed in the absence of water and oxygenated compounds. It was found that the primarily use (as a pre-treatment) of zeolite-based catalyst for the conversion of olefinic feedstock in the OC reaction zone provides a catalyst with significantly improved catalyst performance for the MTO reaction in the XTO reaction zone. Without willing to be bound to any theory, it is believed that the effect consists in a selective poisoning of the non-selective acid sites at the external surface which are responsible typically for side-reaction, resulting in enhanced formation of paraffins. In the present invention we are talking about selectively pre-deactivated catalyst in which the deposited coke has no catalytic activity as is in the case of coke co-catalyst on SAPO-type materials.
Another advantage in using the olefin compositions of this invention for the primarily use of zeolite-based catalyst is that this provides a way to reduce undesirable by-products in the overall conversion of oxygenates to olefins. Typically, heavier olefins such as the C4-C7 olefins are considered as undesirable by-products, because the value of those olefins are considerably lower than ethylene and propylene. Therefore, the by-products of the oxygenate to olefins reaction process can be used to enhance selectivity of the catalyst to provide aromatics and the more desirable ethylene and propylene products.